[PATCH v2 0/6] memcg: disable swap cgroup allocation at swapon

[Jeff Liu <jeff.liu@oracle.com>]

Hello,

Here is the v2 patch set for disabling swap_cgroup structures allocation
per swapon.

In the initial version, one big issue is that I have missed the swap tracking
for the root memcg, thanks Michal pointing it out. :)

In order to solve it, the easiest approach I can think out is to bypass the root
memcg swap accounting during the business and figure it out with some global stats,
which means that we always return 0 per root memcg swap charge/uncharge stage, and
this is inspired by another proposal from Zhengju:
"memcg: Don't account root memcg page statistics -- https://lkml.org/lkml/2013/1/2/71"

Besides that, another major fix is deallocate swap accounting structures on the last
non-root memcg remove after all references to it are gone rather than doing it on
mem_cgroup_destroy().

Any comment are welcome!

v1->v2:
- Refactor swap_cgroup_swapon()/swap_cgroup_prepare(), to make the later can be
  used for allocating buffers per the first non-root memcg creation.
- Bypass root memcg swap statistics, using the global stats to figure it out instead.
- Export nr_swap_files which would be used when creating/freeing swap_cgroup
- Deallocate swap accounting structures on the last non-root memcg removal

Old patch set:
v1:
http://marc.info/?l=linux-mm&m=135461016823964&w=2


Thanks,
-Jeff

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